In wafer fabrication processes such as diffusion, deposition, oxidation and annealing, semiconductor wafers in boats are treated in horizontal tubular chambers encircled with electrical heating elements with heated, toxic, flammable or corrosive gases. A typical horizontal reactor flows a gas into the reactor tube through the source end. The gas is then carried through the tube length and out through exhaust holes. A typical horizontal atmospheric reactor system has process and contamination control problems due to uncontrolled exhaust of reactant and process by-product gases. Due to corrosive nature of most of the gases, exhaust hardware design has been a problem because most metals corrode.
The horizontal reactor tube has two zones: a heated zone and a scavenger zone. The heated zone has several zone elements to heat up the zone and the temperature is typically maintained using proportional-integral-derivative (PID) control. The scavenger zone is an unheated zone which extends from the end of the heating element to the door. The typical horizontal reactor tube has a small hole, typically 1/4" in diameter, near the door end at the bottom. The purpose of the hole is to allow the process by-products to be exhausted to the building exhaust, but undesirable dripping and condensation occurs in the scavenger area as a result. A typical process temperature ranges anywhere from 500.degree. C. to 1225.degree. C. The typical reactor uses a quartz door which fits against the quartz tube directly.
The problems with this typical reactor are numerous. This conventional hardware makes the process not only very dirty but also poses severe corrosion and safety problems due to dripping of hazardous by-products inside and outside the reactor tube. The wide temperature differences between the heated zone and the scavenger zone forces the process by-products to condense and buildup inside the reactor tube extending throughout the length of the scavenger zone. In most applications, this not only causes process drifts due to autodoping created by the buildup, but also makes it necessary to have a frequent cleaning to maintain the process specification. In addition, the wafer load size is limited due to the build up and uncontrolled temperature in the scavenger zone. Usually, the process by-products are very corrosive and there are no compatible materials that can both withstand elevated temperatures, and at the same time cause no metal contamination problems due to corrosion. Hence, there is no direct exhaust/flow control known to date which will address all the above mentioned problems. Improvements in horizontal reactors are necessary to reduce process drifts due to process by-products buildup, to minimize frequency of cleaning, to increase the wafer load capacity of the reactors, and to enhance safety.